In a typical telecommunication network, the central office houses a telephone exchange to which subscriber home and business lines are connected to the network on what is called a local loop. Many of these connections to residential subscribers are typically made using a pair of copper wires, also referred to as a twisted pair, that collectively form a large copper network operated by the telecom provider. Within the central office the line connections between the exchange side and the subscriber side are terminated at a main distribution frame (MDF), which is usually the point where cross-connections between the subscriber lines and the exchange lines are made. Virtually all aspects of the telecommunication network are automated with the notable exception of the copper network. Management of the copper infrastructure is a highly labor intensive process that results in one of the most significant costs faced by telecommunication providers. This is because the central office made traditionally dispatches technicians to the MDF site to manually install cross-connects using jumper wires or to analyze or test the lines in the copper network.
As a result service providers have long desired to reduce the amount of labor required to maintain and manage copper infrastructure by automating the process of making; removing, or modifying cross-connects for line pairs in the MDF. A number of automated cross-connect solutions have been developed and marketed in recent years. Many of these products implement an automated switching matrix using electromechanical relays or robotic technologies to make the cross-connects. A major drawback with the use of electromechanical relays is that their physical size limits the capacity of the switch matrix. In other words, to handle more lines more relays must be added, which is generally very difficult given the space limitations of the matrix. Moreover, robotic solutions tend to exhibit reliability and maintenance issues over the long term that tend to increase costs. While the prior art solutions have existed for some time, none of them have been able to fulfill requirements for cost-effectiveness and scalability required by telecom service providers.
U.S. Pat. No. 4,817,134 discloses an automated switch matrix for cross-connect connecting a set of line pairs within a single plane. The cross-connects on the switch matrix are made using movable shorting elements 24 to electrically connect a first set of line pairs to a second set of perpendicular oriented line pairs. The contact elements are moved into position by rotating positioning screws by two stepper motors operating in combination. The first stepper motor operates to turn a motor positioning screw 37 in order to move the second stepper motor to a desired position in front of the selected shorting element positioning screw 26. The second stepper motor operates to move the shorting element to the cross-connect the line pair. A disadvantage of the switch matrix described is the limited number of line pairs it can cross-connect and lack of scalability to handle growth in the number of lines in the central office. Since the capacity of the switch matrix is designed in from the start it is difficult to add switching capacity as conditions dictate in high-growth markets.
Another drawback is that the switch matrix described does not provide a way to determine the position of the shorting elements. Although it is theoretically possible to calculate position of the shorting elements by counting the stepper motor pulses, the position information would be lost if there is a power outage or if loss of synchronization occurs if the gears slip, for example. Recovering the position information would require moving the contact elements to a reset position thereby causing highly undesirable service interruptions for the existing connections. Without precise position information on the shorting elements it is not possible to perform maintenance functions such as cleaning the contact points by periodically moving the shorting elements slightly back and forth without breaking existing connections. Moreover, the reciprocating action enables the drive elements to be “exercised” during long periods of inactivity, which can increase the service life of the device.
In view of the foregoing, it is desirable to provide an automated switch matrix with a drive mechanism and positioning system that is reliable, economical and overcomes the disadvantages of the prior art.